1. Field of the Invention
The present invention relates to an injector to be used for fuel injection in an engine. More specifically, the present invention relates to an orifice plate disposed at the tip of the injector and used for setting characteristics of fuel injection.
2. Description of Related Art
An electromagnetic injector conventionally used for fuel injection in an engine is typically provided with a seat part at the tip of a nozzle body to cover a valve body formed at the tip of a needle valve from the tip. This seat part is provided with a fuel passage hole, to the tip of which a thin orifice plate having a plurality of orifices (small pores) is attached. Fuel having passed through the fuel passage hole is injected at a predetermined injection angle through those orifices.
Regarding the injector (fuel injection valve) including the above kind of orifice plate, the applicant of the present application has proposed a technique capable of prompting fuel atomization in Japanese patent unexamined publication No. 10-18943.
As shown in FIG. 15, the injector disclosed in the above publication includes a valve body 70a having a conical shape at the tip of a needle valve 70. At the tip of a nozzle body 71, a fuel passage hole 72 is formed. Around the fuel passage hole 72, there is formed a seat part 71a on which the valve body 70a is seated for a valve closed time. Two orifice plates 73 and 74 are fixedly superposed one on top of the other at the tip of the nozzle body 71 to cover the fuel passage hole 72 from the front side (the lower side in FIG. 15). These orifice plates 73 and 74 are provided with a plurality of orifices 73a and 74a, respectively, punched in positions within the fuel passage hole 72. These orifices 73a and 74a, as shown in FIG. 16, are formed each having a central axis C1, C2, C3, or C4 at an angle with a central axis O of the fuel passage hole 72 so that each distance between the axes C1 and C2 and between the axes C3 and C4 is widened downward. Thus, the orifices 73a and 74a are formed inclining to be oblique to each surface of the orifice plates 73 and 74. These orifices 73a and 74a are arranged in corresponding positions in the two orifice plates 73 and 74 respectively and have an equal inner diameter. The orifices 73a and 74a being inclined as above have stepped parts 75 on a superposed surface, namely, a joint portion between the orifices 73a and 74a. By this stepped part 75, the fuel flow passage provided by the orifices 73a and 74a is narrowed at the joint portion between the orifices 73a and 74a in a fuel injecting direction. Fuel to be sprayed will therefore impinge upon the stepped parts 75, so that the flow of fuel becomes turbulent. This turbulent fuel is utilized to prompt atomization of the fuel to be injected.
However, the orifice plates 73 and 74 of the conventional injector disclosed in the above publication need manufacturing to have the inclined orifices 73a and 74a, which would make it difficult to machine the plates 73 and 74 with accuracy. This conventional technique, in addition, requires forming of a plurality of orifices 73a or 74a inclined in different directions in each single orifice plate 73 and 74, as shown in FIG. 17. This would increase the number of machining steps due to punching of the orifices 73a and 74a, leading to a problem of productivity.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide an orifice plate which can facilitate machining for providing an inclination to fuel to be injected through an orifice.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided an orifice plate which is mounted at a tip of an injector to cover a fuel passage hole formed at the tip, the orifice plate including: a plate body constructed in layers; and an orifice for allowing fuel having passed through the fuel passage hole to be injected; wherein the orifice is constructed of a plurality of holes each formed in each layer of the plate body so that each hole is perpendicular to a surface of the plate body, the holes being disposed in communication with each other and with displacements from each other along a line obliquely intersecting the plate body.
According to another aspect of the invention, there is provided an injector provided with the orifice plate described above, wherein the injector includes a plate holder provided with an injection hole, and the orifice plate is fixedly pressed against the tip of the injector by means of the plate holder and the orifice is positioned within the injection hole.